1. Technical Field
The present invention relates to an illumination device and a liquid crystal display apparatus, and more specifically, to an illumination device and a liquid crystal display apparatus including a flexible wired board having a light source member mounted one of principal planes thereof.
2. Related Art
In general, an illumination device which outputs light emitted from a light source to a predetermined direction by guiding the light by a light guide member formed of translucent material such as acrylic is known as an illumination device which outputs light emitted from a light emitting diode (hereinafter referred to as “LED), which corresponds to the light source, to a predetermined direction.
Such illumination device is used, for example, as a backlight unit of a side light type in the liquid crystal display apparatus. The backlight unit of the side light type is mainly configured by disposing LEDs on the side surfaces of a light guide panel of a flat plate shape, which corresponds to a light guide member, and outputs light emitted from the LEDs and incoming from the side surfaces of the light guide panel through a principal plane as an exit plane in a direction of the thickness of the light guide panel (in the direction of the normal line of the principal plane of the light guide panel). An optical sheet such as a diffuser panel and a prism sheet is disposed on the exit plane of the light guide panel to diffuse light outputted from the light guide panel substantially evenly into a plane.
In the liquid crystal display apparatus, a transmissive liquid crystal panel is disposed on the side of an observer of the backlight unit, so that light outputted from the backlight unit is modulated by the transmissive liquid crystal panel and is outputted toward the observer, so that display on the liquid crystal display apparatus is achieved.
In the backlight unit as the illumination device as described above, a flexible printed circuit board (hereinafter, referred to as “FPC”) which is a flexible wired board having an LED mounted on a mounting surface thereof is used for the purpose of downsizing and weight reduction. The FPC is stuck to a light guide panel or a casing via adhesive agent such as a double-faced adhesive tape (double-faced adhesive sheet). Since the FPC is partly translucent and has a light transmitting property, light emitted from the LEDs passes through the FPC, and outputted from different positions from an exit plane of illumination light of the backlight unit as stray light. With such stray light, uneven distribution is generated in luminance of the backlight unit, and hence the display quality of the liquid crystal display apparatus is lowered.
In order to prevent the light emitted from the LEDs from passing through and leaking from the FPC, for example, in a light source of a backlight in a liquid crystal display apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2003-156739, a light-shielding sheet having a light-shielding property is stuck and fixed to the surface of the FPC on the opposite side from the surface on which the LEDs are mounted via adhesive agent such as double-faced adhesive tape.
As disclosed in Japanese Unexamined Patent Application Publication No. 2003-156739, when the light-shielding sheet is stuck on the surface of the FPC with adhesive agent, when the FPC comes apart from the light-shielding sheet, a bending stress is applied to the FPC. For example, when defects such as uneven luminance, entry of foreign substances, scratch or deformation of members caused by displacement of the fixed position of the LEDs are found after the FPC and the light-shielding sheet is stuck together, it is necessary to perform rework to peel off the light-shielding sheet stuck on the FPC, and then repair the failed portions. When peeling off the light-shielding sheet stuck on the FPC in this manner, the FPC stuck to the casing of the backlight unit or the light guide panel comes apart as well by being pulled by the light-shielding sheet.
At this time, since the FPC has flexibility, the FPC is deformed according to a peeling force. However, since the LEDs mounted on the FPC have no flexibility, if the FPC is deformed, there is a problem such that an excessive stress is applied to joint portions between terminals of the LEDs and the FPC by soldering, and the joint portions may be separated or cracked.
In the case in which separation or cracking is occurred at the joint portions with respect to the terminals of the LEDs, it is necessary to replace the FPC. Even when the cracking does not occur, application of the excessive stress on the terminals of the LEDs must be avoided since it may cause defective illumination of the LEDs.